This invention relates in general to a non-contact distance measuring device, and more particularly to an apparatus for indicating the position of a flexible web which may be otherwise disturbed by a contact measuring device.
The standard methods used to measure distance between two solid surfaces may not be applicable when one of the surfaces is not rigid, as in the case of a film belt. In the current art, a contact method is used, wherein a measuring device contacts the belt as disclosed for example in U.S. Pat. No. 5,956,544. However, the contact method may cause the belt to be deflected, thereby introducing an error in the measurement.
In addition, contact may damage sensitive surfaces. For example, prior methods used to determine the distance between an electrometer probe and the film belt in a copier, or printer, is by physical contact with both surfaces. This is done with a setup film, which is then replaced before the unit is shipped. When an optical based system, such as a laser, is used, the energy of a reflected beam is currently used to calculate the distance. Any changes in the target surface, such as dirt or scratches, will affect the amount of energy reflected, therefore resulting in an inaccurate measurement. Therefore, a non-contact method is required which is not susceptible to errors resulting from the loss of reflected energy.
The present invention provides a non-contacting apparatus for determining the distance between a reference point and a target surface, wherein a collimated beam such as a laser beam is reflected off the target surface and viewed on an imaging member such as a viewing window or screen. A source of the collimated beam and a screen are contained in a single housing. The projection angle of the beam and the location of the screen can be preset for the desired distance between the surfaces. The location of the reflected beam relative to markings on the screen indicate whether the distance is within specifications. Using a combination of both horizontal and vertical lines on the screen allows confirmation of both the distance and angular alignment of the target to the reference point. Mirrors may also be used to configure a beam path for the system. As the location of the reflected beam on the screen is used to determine the distance rather than the amount of reflected energy, changes in the surface of the target do not affect the accuracy of the system.
For example, this tool would be put in place of the electrometer probe in an electrophotographic marking engine such as a copier/printer, to aid in the set up or confirmation of the spacing between the probe and a film belt. A visible laser source, i.e. a laser diode, is employed to eliminate external connections for operation. This system can also be applied to other measurements where conventional methods are not practical. An example could be the spacing between the tones roller and photoconductor in a copier/printer, or the gap between the grid of a charger and the film belt. Alternative configurations of this tool would allow for manual adjustment of the beam source and/or mirrors to measure different distances.
The invention, and its objects and advantages, will become more apparent in the detailed description of preferred embodiments presented below.